Re: Business case for APIs?
This is all IMHO:
APIs are useful if you have an application which you want to increase the usage of by allowing it to be embedded in other applications, or to be automated.
Email marketing systems are great examples. They're useful in their normal usage...a human clicks around the site, creating lists and content, and eventually clicking "send". But, when they got the API religion, they became exponentially more useful. With available, easy APIs, developers started using them instead of
$mail = open (MAIL, "|/usr/lib/sendmail -S $subject");
So, if you can provide greater functionality than the way developers are doing it now, for a reasonable price, you'll expand the market footprint of your application with a web API.